1. Field of the Invention
The present invention pertains to a system for positioning certain downhole tools in wellbores using coiled metal tubing having an electrical cable or wireline disposed therein and including connector apparatus at each end of the tubing for supporting the downhole tool and providing a take off point for the electrical cable, respectively.
2. Background
In various downhole operations in wellbores for producing hydrocarbon fluids certain difficulties arise in positioning downhole tools, particularly in deviated wells. For example, various types of electrically operated downhole tools, such as logging sondes and perforating tools, are usually lowered into the wellbore at the end of a flexible armored cable or wireline. In deviated wells, in particular, the positioning of downhole tools at the end of a flexible cable such as a wireline, can become particularly difficult since gravity alone may not be sufficient to lower the tool into the desired position in the wellbore. Moreover, if the tool tends to become stuck or resists pull-out operations, the wireline cable will stretch much like a rubber band before the holding force is overcome such that the performance of logging operations, for example, may be highly inaccurate.
In this regard, it has been suggested to position downhole tools with a somewhat more rigid positioning member such as coilable metal tubing which is used in various other types of well operations. U.S. Pat. No. 3,401,749 to W. L. Daniel, for example, suggests positioning a logging tool in a deviated wellbore using coilable metal tubing within which the wireline cable is extended. However, certain problems associated with positioning downhole tools with coilable tubing have heretofore been unsolved. Among those problems is locating or centering a logging tool, for example, in the wellbore, which may be impossible if the tool is rigidly connected to the relatively inflexible tubing. Moreover, with prior art arrangements, moving logging and other types of downhole tools into and out of deviated wellbores using coilable tubing also results in urging the tool against the side of the wellbore with such force as to risk damage to the tool or the wellbore and to prevent desired positioning of the tool.
Other problems associated with positioning down-hole tools in wellbores using coilable tubing include providing suitable means for separation of the wireline cable at a location which will permit retrieval or fishing operations to be carried out and to prevent the possible accumulation of several hundred feet of wireline piled on top of the logging tool in the event of cable failure at a point substantially uphole from the tool itself. There are several other problems and desiderata which have been solved and have been provided by the apparatus and method of the present invention as will be further appreciated by those skilled in the art.